A boy aged around 14 raped an elderly woman in her own home after knocking on her door asking if he could talk to her about the war, police said.
Detectives said the teenager carried out the "calculated and horrifying" attack on the pensioner, aged in her 70s, in Hardwick, Banbury, Oxfordshire.
He called at her home at around 9am on Saturday asking if she could share stories about the war and the elderly with him. But once inside, he pushed her to the floor and raped her.
The victim activated her personal care alarm and the boy ran off. Thames Valley Police were alerted to the rape at 9.20am by the alarm company.
Detective Sergeant Andrew Thompson said: "This was a calculated and horrifying attack, with the young boy talking his way into the victim's house deliberately to sexually assault her.
"I am very keen to speak to anyone who saw the boy in the area on Saturday, or may have had a visit from him over the weekend asking questions about the war.
"I would also like to speak to anyone who recognises his description or who has any information which may help us catch the person responsible for this despicable crime."
Superintendent Andy Boyd said: "This was a very distressing incident and I would like to reassure residents that a team of detectives are working hard to catch the person responsible.
"Neighbourhood officers will be carrying out reassurance patrols in the Hardwick area and handing out leaflets to concerned residents."
The boy is described as white, aged between 14 and 16 years old, with short, dark brown hair. He was wearing a zip-up jacket and jeans slung low on his waist.
Anyone with information is asked to call Thames Valley Police on 101 or Crimestoppers anonymously on 0800 555 111.